Ripl radio interferometric planet search
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RIPL Radio Interferometric Planet Search. Geoffrey Bower UC Berkeley. Collaborators: Alberto Bolatto (UMD), Eric Ford (UFL), Paul Kalas, Anna Treaster, Vince Viscomi (UCB). MM Wavelength T Tauri Outburst in Orion. 2 nd most luminous stellar radio outburst

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RIPL Radio Interferometric Planet Search

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RIPLRadio Interferometric Planet Search

Geoffrey Bower

UC Berkeley

Collaborators: Alberto Bolatto (UMD), Eric Ford (UFL),

Paul Kalas, Anna Treaster, Vince Viscomi (UCB)


MM Wavelength T Tauri Outburst in Orion

  • 2nd most luminous stellar radio outburst

  • Briefly, brightest object in nebula

  • Required long baselines for detection

  • Magnetized T Tauri outburst

  • Contemporaneous with X-ray outburst

  • Many such objects likely to be found by CARMA & ALMA

BIMA A configuration images

(Bower, Plambeck, Bolatto, Graham, de Pater, McCrady, Baganoff 2004)


Orion Nebula Parallaxw/Star GMR-A

D=389 pc +/- 5%

<0.1 mas/epoch

Sandstrom, Peek, Bower, Bolatto,

Plambeck 2007

Astro-ph/0706.2361


Planets are Easy to Detect


Companion to GJ 752B Detected w/Optical Astrometry

Pravdo & Shaklan 2009


White et al


Gudel 2002


Requirements of a Planet Survey

  • Low mass, nearby star

    • Astrometric displacement ~ 1 mas

  • Nonthermal radio emission

    • S ~ 1 mJy

    • F ~ GHz

    • Positional stability < 0.1 mas

  • Stable Image

    • Active, but not too active


VLA M dwarf Flux Survey

  • 174 X-ray selected nearby M dwarfs

  • 10 minute VLA observations with 50 microJy rms

  • 40 detections of 29 stars

  • Rough agreement X-ray-radio correlation

  • No distinction between early and late types

Bower, Bolatto, Ford, Kalas 2009, ApJ, in press


Stars are Variable

EV Lac

Osten et al 2005


Pilot Survey

  • 7 stars

  • 3 epochs

  • < 10 days

    • Hipparcos errors ~ 1 mas/y

    • Error over 10 days < 0.1 mas

  • Test

    • Detectability

    • Image stability

8000 km baselines

3 cm wavelength

1 mas resolution

Astrometry ~ beam/SNR


Results from Pilot Study:Apparent Motion of GJ 4247

15 mas

26 March 2006

25 March 2006

23 March 2006

Comparison of radio positions (points) with predictions from Hipparcos astrometry (solid line) reveal noise-limited rms residuals ~0.1 milliarcseconds, approximately 1 stellar diameter.

Bower, Bolatto, Ford, Kalas 2009, ApJ, in press


Pilot Study Results

GJ 4247

GJ 896A

Residuals are sensitivity limited

~0.2 mas

GJ 65B


VPAS Results


Results from Pilot Study:Constraints on Companion Masses

Planet Mass (Mjup)

Semi-major Axis (AU)

  • Agreement with optical astrometry sets upper limit on acceleration and therefore companion masses

    • Mp < 3 – 10 MJup @ 1 AU

  • Sensitivity is limited by the short lever arm of VLBA observations: ~10 days

  • RIPL will extend this lever arm by factor of 100

Bower, Bolatto, Ford, Kalas 2009, ApJ, in press


RIPLRadio Interferometric Planet Search

  • 30 stars

  • 12 epochs/4 years

  • VLBA + GBT

  • 512 Mb/s

  • 2 hours on source + 2 hours calibration

  • 25 microJy rms

    • 4 x lower than pilot survey

  • 1392 hours total

Key question: What is fraction of long-period planets around low mass stars?


RIPL Sample

  • 30 Stars

  • M1 – M8

  • V = 9.6 – 15.8 mag

  • S_6cm = 0.1 – 6 mJy

  • D = 2.7 – 9.5 pc

  • 11 are members of known binary or multiple systems


Simulated RIPL Results


RIPL Sensitivity


Current Status

  • Observing began Oct 2007

    • Approximately 4 observations/month

  • Expected completion in mid-2011

  • 40% complete

  • Pipeline processing underway (see poster by Vince Viscomi)

  • All stars detected

    • 60% of stars detected in every epoch


Benefits of Astrometric Detection

  • Unique method

  • Breaks degeneracy of RV searches for mass, inclination angle, and ascending node

  • Probes low mass, active stars that are difficult to study with RV method

  • Planet fraction of low mass stars poorly determined

  • Detects planets that can be studied with extreme AO

  • Ties radio and optical astrometric reference frame


RV Search ResultsFew M dwarf Hosts


RV Search ResultsMost Planets are >10 pc Distant


RV Search ResultsWhat is Mplanet/Mstar?


Microlensing Search Results What is Mplanet/Mstar?


Microlensing Search ResultsPlanets are Very Distant


Comparative Sensitivity of Searches


Future Directions for Radio Astrometry & Planets

  • Bandwidth upgrade for VLBA

    • 512 Mb/s  8 Gb/s

    • 4 x sensitivity

    • Calibrator density increases by 8 x

    • In-beam calibrators

    • 10 microarcsec accuracy  Neptune mass planets

  • Square Kilometer Array

    • 100 x sensitivity

    • 3000-5000 km baselines

    • 1 microarcsec accuracy  Earth mass sensitivity


Summary

  • Radio astrometry is sensitive to sub-Jupiter mass planets around M dwarfs

  • We can already exclude BD companions to three stars based on only three measurements

  • RIPL survey will probe low mass, active star parameter space


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